[BUG] Failed to use fast mode in opus 4.7 when using LLM Gateway

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Unable to toggle opus 4.7 fast mode. I am on max 20 plan and already enable extra usage.

<img width="1444" height="355" alt="Image" src="https://github.com/user-attachments/assets/57ca72fc-ab18-420b-a204-8ea3c3118e61" />

What Should Happen?

Should be able to

Error Messages/Logs

Steps to Reproduce

with custom ANTHROPIC_BASE_URL and ANTHROPIC_AUTH_TOKEN

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.142

Platform

Other

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

_No response_